The present invention provides a method for an efficient and sanitary treatment of brown grease.
Grease is a material, either liquid or solid, composed primarily of fats, oils and grease (also referred to as FOG) from animal or vegetable sources. Brown grease (or trap grease) is waste that is recovered from grease traps and interceptors. Yellow grease is oil and grease that comes directly from fryers and other cooking equipment. A grease trap is a small volume device located inside a food service facility, generally under a sink, designed to collect, contain, or remove food wastes and brown grease from the waste stream while allowing the balance of the liquid waste to discharge into the wastewater collection system, usually a sanitary sewer system. A grease interceptor is a large volume device located underground and outside of a food service facility designed to collect, contain or remove food wastes and brown grease from the waste stream while allowing the balance of the liquid waste to discharge to the wastewater collection system, usually a sanitary sewer system. Interceptors have at least one inspection hatch on the top surface to facilitate inspection, cleaning and maintenance by a service provider.
The terms “grease trap” and “grease interceptor” are often used interchangeably in the literature. For this document, discussion of any “grease separation device” refers to both types of units without need for differentiation. For this document, FOG refers to Brown Grease unless otherwise noted.
A problem today is that the nature of FOG is changing and this change is leading to problems in the effective treatment of FOG. While once largely composed of animal fats (such as lard), now fats, oils, and grease (FOG) the waste grease and oils that are discharged from kitchen drains into sanitary sewer systems are now principally manufactured vegetable oils designed to adhere to food. The basic chemical structure of FOG is varying combinations of glycerol (C3H8O3) and fatty acids (chains of carbon-hydrogen with a carboxylic group—COOH—attached). However, as food science advances, and cooking oils become more and more efficient, the fatty acid chains become much more complex. Unlike the older, animal fat-based cooking media, the more complex fatty acids are by and large more stable, and they are less likely to break down either in the sanitary drain system, from the activity of naturally occurring bacteria, or from general exposure in the open environment.
Both animal fats and vegetable oils are 8-12 percent lighter than water and do not mix with it. FOG forms a floating layer on the water in the grease separation devices, and that property enables those lighter materials to be efficiently removed, essentially by vacuuming out the floating fats and as much of the water as regulations require.
The increased development of central business districts encircled by suburban areas, the increasing mobility of our society, and increased restaurant patronage per capital per year have led to significant growth in the commercial food sector. These trends have led to the increase of commercial areas containing high densities of restaurants, mall food courts, and supermarket ready-to-eat meals. Additionally, many other new food preparation facilities such as sports arenas, strip shopping centers, convenience stores and carry-out kiosks have raised the numbers of high-loading grease sources on municipal sewer systems. With more restaurants, institutional kitchens, and other commercial, food handling venues, the nation's sewer systems experience increasing difficulty with grease clogged sewer lines and pumping stations affecting sewage treatment operations.
A major area of problems is between the source of the FOG and the treatment plant. Drainage pipes within buildings are usually made from metals or plastics. Municipal sewer piping may be made from metals, plastics or ceramic materials such as terra cotta. All of these materials are hydrophobic and oleophilic. Hydrophobic means water does not stick to the material, a good property for water-handling pipes. Oleophilic means oily substances are naturally attracted to the material, which is why piping encounters grease clogging.
Fats and oils naturally stick to piping walls. However, fats and oils also possess an inherent surface “stickiness” (increasingly an engineered property to enhance cooking properties), which leads to sewage-borne solids sticking to the grease layer on a sewer pipe's inside walls, slowly and relentlessly reducing the pipe's transfer capacity. This frequently leads to a pipe becoming so clogged that the effluent in the line emerges through a manhole (or burst pipe) to the surface as a sanitary sewer overflow (SSO). Not only is this a health hazard, but local governments can be, and are, fined by the EPA for such spills. Additionally, the remedy for the clogged mains, physically cleaning the pipe systems, is expensive, messy, and dangerous work.
For these reasons, regulators from the EPA at the federal level to state, county, and municipal governments have increasingly implemented policies and regulations to control the influx of FOG into the public wastewater systems. The most common and generally preferred methods of FOG entrapment is either a grease trap (for small establishments) or grease interceptors (for mainline, higher volume establishments). These regulations generally specify sizing criteria and frequently mandate grease removal (i.e. service call) frequency.
In addition to companies that provide extraction of interceptor contents as their service there are an array of products that are purported to clean and maintain grease interceptors. However, these existing products related to cleaning and maintaining grease interceptors have some drawbacks to their use.
The first of these products are enzymes. Basically, an enzyme is a protein that will act on a compound and break it into several smaller compounds. Enzymes are compound specific; in fact, there are enzymes that will work only on the compounds found in FOG. Although the actual enzymatic action is quite complex, the end result is that the fatty acids are severed from the glycerol base. This allows the FOG to dissolve and move downstream. However, enzyme reactions are all reversible chemical reactions. The free fatty acids can re-join the glycerol base and become FOG, complete with the same characteristics it once had. While enzymes may dissolve FOG and facilitate its dispersal from the grease interceptor, (and this may be beneficial to the restaurant owner in that the grease interceptor may not need to be pumped as frequently) the FOG problem is just displaced. It will re-appear as the fatty acids and glycerol recombine in a sewer or in a pump station's wet well downstream. Thus the disposal problem is simply transferred to the public sector. In addition, enzymes do not replicate themselves. They will be carried out along with the dissolved grease. As a result, enzymes must be frequently introduced into the grease interceptor, representing an ongoing maintenance issue for management.
The second of these products are detergents. Detergents are not an effective treatment option. They may clean blockages from the restaurant's lines, but create other problems for a sewer system and its wastewater treatment plant. In a similar fashion to enzymes, they break up grease deposits, but the grease can re-congeal further downstream in the collection system.
The third of these products are bacteria and solvents. Using bacteria to consume sewer grease is effective only when the proper microorganisms are used and applied through a highly developed service system. Bacteria products commonly sold with “do-it-all” claims typically give grease interceptor owners a false sense of security. Bacteria are pH and temperature sensitive and do not maintain their replicating activity particularly well in the (low pH) environment found in grease interceptors. Also, their use is generally not well received by (publicly owned treatment works (POTWs).
Finally, many distributors of biological liquefiers, enzymes, and other such products claim that their products will eliminate the need to pump a grease interceptor ever again. Some of the products that claim to be bacterial products are actually inactive forms of bacteria packed in solvents such as kerosene, toluene, terpene, surfactants, etc. It is actually the solvent, not the bacteria, which dissolves the grease. This defeats the purpose of a grease interceptor. The product may move FOG out of the food processor's grease interceptor, but the grease can quickly recongeal in the POTW's collection system. In summary, these alternatives are not a solution and many sanitary system operators do not condone their use.
Disposal options in the realms of bio-diesel fuel manufacture and bio-fuel (heating fuels and turbine feeds for example) are interesting research projects but are generally experimental or limited in scope, and exhibit increased costs compared to petroleum based fuel. A 2% mix of bio-diesel with conventional diesel adds about three cents per gallon at the pump and trucking organizations are resistant to mandated use of these mixes. In any case, yellow grease, not brown grease, is the preferred feedstock for bio-fuels. Brown grease has, however, been the subject of specific research for its use as a feedstock for bio-diesel fuel manufacture. Much of the work has been done at the university level, though at least one large rendering company has a functioning production plant, Griffin Industries, Inc., Cincinnati, Ohio, that may use a small amount of brown grease in its feed. Several issues, however, indicate that brown grease will be very slow to catch on as a large-scale feedstock.
Bio-diesel feedstock demands low free fatty acid content. Brown grease contains 5-times (or more) free fatty acids (FFAs) as soy oil (or other low FFA oils that are processed with alkaline catalysts into bio-fuels) so must be blended with low FFA components to make bio-diesel feed.
The large scale alternative for brown grease processing is a relatively complex acid catalyst process demanding high-energy drying and high temperature processing at high pressures, demanding acid resistant steels and other specialized handing equipment.
New EPA directions towards 100% pumping rules mean that the brown grease requires separation from massive amounts of water, and exceedingly low water content in the feed product is a requirement for processing; slightly too much water and the alkaline catalyst procedure for bio-diesel production produces a soap contaminate in the bio-fuel. Eliminating water is energy intensive, thus low water “yellow grease” or virgin vegetable oils are highly preferred as feedstock.
Research on effective brown grease utilization has not translated into effective large-scale operations. The issue of disposal of contaminants entrained in the grease-sludge waste from bio-diesel production still remains.